console.log('------------------------------------------------------');
const arr = ['red','green','blue'];
console.log(arr.toString());//"red,green,blue"
console.log(arr.valueOf());//[ 'red', 'green', 'blue' ]
let person_1 = {
    toString:function(){
        return 'toString_Marry';
    },
    toLocaleString:function(){
        return 'toLocaleString_Marry';
    }
}
let person_2 = {
    toString:function(){
        return 'toString_Smith';
    },
    toLocaleString:function(){
        return 'toLocaleString_Smith';
    }
}
let list = [person_1,null,person_2,,undefined];
console.log(list.toString());//toString_Marry,,toString_Smith,
console.log(list.toLocaleString());//toLocaleString_Marry,,toLocaleString_Smith,,